Comparative 16S rRNA gene sequence analysis and major physiological differences indicate two distinct sublineages within the genus Azoarcus: the Azoarcus evansii lineage, comprising Azoarcus evansii (type strain KB740 T =DSM 6898 T =CIP 109473 T =NBRC 107771 T), Azoarcus buckelii (type strain U120 T =DSM 14744 T =LMG 26916 T), Azoarcus anaerobius (type strain LuFRes1 T =DSM 12081 T =LMG 30943 T), Azoarcus tolulyticus (type strain Tol-4 T =ATCC 51758 T =CIP 109470 T), Azoarcus toluvorans (type strain Td21 T =ATCC 700604 T =DSM 15124 T) and Azoarcus toluclasticus (type strain MF63 T =ATCC 700605 T), and the Azoarcus indigens lineage, comprising Azoarcus indigens (type strain VB32 T =ATCC 51398 T =LMG 9092 T), Azoarcus communis (type strain SWub3 T =ATCC 51397 T =LMG 9095 T) and Azoarcus olearius (type strain DQS-4 T =BCRC 80407 T =KCTC 23918 T =LMG 26893 T). Az. evansii lineage members have remarkable anaerobic degradation capacities encompassing a multitude of alkylbenzenes, aromatic compounds and monoterpenes, often involving novel biochemical reactions. In contrast, Az. indigens lineage members are diazotrophic endophytes lacking these catabolic capacities. It is proposed that species of the Az. evansii lineage should be classified in a novel genus, Aromatoleum gen. nov. Finally, based on the literature and new growth, DNA-DNA hybridization and proteomic data, the following five new species are proposed: Aromatoleum aromaticum sp. nov. (type strain EbN1 T =DSM 19018 T =LMG 30748 T and strain pCyN1=DSM 19016=LMG 31004), Aromatoleum petrolei sp. nov. (type strain ToN1 T =DSM 19019 T =LMG 30746 T), Aromatoleumbremense sp. nov. (type strain PbN1 T =DSM 19017 T =LMG 31005 T), Aromatoleum toluolicum sp. nov. (type strain T T =DSM 19020 T =LMG 30751 T) and Aromatoleum diolicum sp. nov. (type strain 22Lin T =DSM 15408 T =LMG 30750 T).

Deep Lake, Antarctica, is a hypersaline lake characterized by a very low microbial diversity, dominated by archaea, and a lack of grazing organisms, making viruses important players in regulating community structure. Here we present an in-depth characterization of an archaeal virus-host system isolated from Deep Lake. Upon purifying the environmental virus lysate through plaque assays, with the intention to generate a clean and stable virus-host system, we select for a virus variant with an exclusively lytic life cycle (HRTV-DL1). The host Halorubrum lacusprofundi exhibits a large arsenal of virus exclusion mechanisms, indicating a long ongoing arms race with viruses. However, we uncover that the majority of this arsenal was lost spontaneously in a strain grown under non-challenging laboratory conditions. By challenging both the parental strain and the sensitive strain with HRTV-DL1, we discovered a number of putative virus exclusion mechanisms that are only activated in the sensitive strain upon the lack of defense systems present in the parental strain. We identify one of two S-layer proteins as primary receptor for HRTV-DL1 and conclude that the presence of two different S-layer proteins in one strain provides a strong advantage in the arms race with viruses. We propose the involvement of origin recognition proteins (ORC1/CDC6) in virus exclusion. While Hrr. lacusprofundi and HRTV-DL1 represent a great archaeal model system to observe the arms race between viruses and hosts, our work also demonstrates that an isolated model virus-host systems does not reflect the entire spectrum of interactions as they occur in the environment.

Summary Large quantities of organic matter are continuously deposited, and (a)biotic gradients intersect in the soil–rhizosphere, where biodegradation contributes to the global cycles of elements. The betaproteobacterial genus Aromatoleum comprises cosmopolitan, facultative denitrifying degradation specialists. Aromatoleum aromaticum. pCyN1 stands out for anaerobically decomposing plant‐derived monoterpenes in addition to monoaromatic hydrocarbons, polar aromatics and aliphatics. The catabolic network's structure and flexibility in A. aromaticum pCyN1 were studied across 34 growth conditions by superimposing proteome profiles onto the manually annotated 4.37 Mbp genome. Strain pCyN1 employs three fundamentally different enzymes for C–H‐bond cleavage at the methyl groups of p‐cymene/4‐ethyltoluene, toluene and p‐cresol respectively. Regulation of degradation modules displayed substrate specificities ranging from narrow (toluene and cyclohexane carboxylate) via medium‐wide (one module shared by p‐cymene, 4‐ethyltoluene, α‐phellandrene, α‐terpinene, γ‐terpinene and limonene) to broad (central benzoyl‐CoA pathway serving 16 aromatic substrates). Remarkably, three variants of ATP‐dependent (class I) benzoyl‐CoA reductase and four different β‐oxidation routes establish a degradation hub that accommodates the substrate diversity. The respiratory system displayed several conspicuous profiles, e.g. the presence of nitrous oxide reductase under oxic and of low‐affinity oxidase under anoxic conditions. Overall, nutritional versatility in conjunction with network regulation endow A. aromaticum pCyN1 with broad adaptability.

Aromatic compounds are abundant constituents not only of natural organic matter but also of bulk industrial chemicals and fuel components of environmental concern. Considering the widespread occurrence of redox gradients in the biosphere, facultative anaerobic degradation specialists can be assumed to play a prominent role in the natural mineralization of organic matter and in bioremediation at contaminated sites.